Low Power Radio Device With Reduced Interference

ABSTRACT

A low power radio device, operable in a first radio system, comprising: a detector for detecting the polarization of an antenna of a further radio device, operating in a further radio system, different to the first radio system; and a transmitter for controlling the polarization of a transmitted radio signal in dependence on the detected polarization. The polarization of the transmitted signal may be controlled to be substantially orthogonal to the polarization of the antenna of the further radio device.

FIELD OF THE INVENTION

Embodiments of the present invention relate to a low power radio device.In particular, they relate to a low power radio device for use in aradio system that operates using Ultra Wide Bandwidth (UWB) signals orany other wideband radio frequency system.

BACKGROUND TO THE INVENTION

UWB is a wireless radio technology. A UWB transmitter works by sending asignal across a very wide spectrum of frequencies. A correspondingreceiver translates the signal into data. UWB technology may be definedas any radio technology having a spectrum that occupies a bandwidthgreater than 20% of the centre frequency, or a bandwidth of at least 500MHz.

UWB is typically suited for transmitting data between consumerelectronics, personal computers and mobile devices. UWB has the capacityto handle very high bandwidths of data, at very high speeds across shortranges. For example, UWB devices may be used to transport multiple audioor video streams.

An example of a standard that incorporates UWB is the Wireless UniversalSerial Bus (WUSB) Specification, Revision 1.0. WUSB aims to provide adata rate of 480 Mbps over a distance of 3 metres and 110 Mbps over adistance of 10 metres.

In the United States, the Federal Communications Commission (FCC) hasmandated that UWB radio transmissions can legally operate in thefrequency range 3.1 GHZ to 10.6 GHz, at a limited transmit power of−41.3 dBm/MHz. UWB radio transmissions can also legally operate in thefrequency range 1 GHz to 3.1 Ghz, but at a lower power than those in the3.1 GHZ to 10.6 GHz range.

The GSM cellular system operates at approximate frequencies of 850, 900,1800 and 1900 MHz. As UWB devices may emit radiowaves in the frequencyrange 1 GHz to 3.1 GHz, they may cause interference to mobile terminalsusing some GSM frequencies, and/or some WCDMA frequencies and/or 802.11gfrequencies or Bluetooth frequencies. The large bandwidth used in UWBdevices means that UWB transmissions having a centre frequency 500 MHzor more away from the GSM frequencies may still cause interference.

Furthermore, it is currently envisaged that the fourth generation ofradio telephone systems (4G) will operate somewhere in the frequencyrange 3 GHz to 5 GHz. As UWB devices are allowed to operate in thefrequency range of 3.1 GHZ to 10.6 GHz, it is envisaged that UWB devicesmay cause interference at 4G mobile terminals.

BRIEF DESCRIPTION OF THE INVENTION

According to first aspect of the present invention, there is provided alow power radio device, operable in a first radio system, comprising: adetector for detecting the polarization of an antenna of a further radiodevice, operating in a further radio system, different to the firstradio system; and a transmitter for controlling the polarization of atransmitted radio signal in dependence on the detected polarization.

According to a second aspect of the present invention, there is provideda method for controlling the polarization of a transmitted signal for afirst low power radio system, comprising the steps of: detecting thepolarization of an antenna of a radio device, operating in a furtherradio system, different to the first low power radio system; andcontrolling the polarization of a transmitted radio signal for the firstlow power radio system in dependence on the detected polarization.

According to a third aspect of the present invention, there is provideda computer program for use in a low power radio device having an antennafor receiving radio signals comprising two non-parallel elements, thecomputer program comprising: means for receiving a first signal from afirst antenna element and for receiving a second signal from a secondantenna element; means for processing the received first and secondsignals to determine the polarization of a radio signal incident uponthe antenna; means for changing the effective polarization of theantenna to change the polarization of low power radio signalstransmitted by the antenna in dependence on the polarization of theincident radio signal.

In embodiments of the present invention, a low power radio device isadvantageously able to reduce the amount of interference it causes at afurther radio device when it transmits a radio signal, by: a) detectingthe polarization of an antenna of a further radio device, and b)controlling the polarization of a radio signal it transmits independence on the detected polarization.

Typically, a low power radio device is a device that is operable totransmit signals with a maximum range of 100 metres or less, and/orreceive radio signals that have been transmitted with a maximum range of100 metres or less. In particular, some low power radio devices areoperable to transmit signals with a maximum range of 10 metres or less,and/or receive radio signals that have been transmitted with a maximumrange of 10 metres or less. UWB devices are often operable to transmitsignals with a maximum range of 3 metres or less, and/or receive radiosignals that have been transmitted with a maximum range of 3 metres orless.

According to a fourth aspect of the present invention, there is providedan arrangement comprising a first low power radio device and a secondlow power radio device, operable in a first radio system, wherein: thefirst low power radio device comprises: a detector for detecting thepolarization of an antenna of a further radio device, operating in afurther radio system, different to the first radio system; and atransmitter for controlling the polarization of a transmitted radiosignal in dependence on the detected polarization; and the second lowpower radio device comprises: a receiver for receiving a radio signal;and a transmitter for controlling the polarization of a transmittedradio signal in dependence on the polarization of the received radiosignal.

According to a fifth aspect of the present invention there is provided amethod for controlling the polarization of radio signals for a firstradio system including a first low power radio device and a second lowpower radio device, comprising the steps of: a first low power radiodevice detecting a polarization of an antenna of a further radio device,operating in a further radio system, different to the first radiosystem; the first low power radio device controlling a polarization of atransmitted radio signal in dependence on the detected polarization; asecond low power radio device receiving a radio signal; and the secondlow power radio device controlling a polarization of a transmitted radiosignal in dependence on the polarization of the received radio signal.

Advantageously, in embodiments of the present invention, the amount ofinterference caused at a further radio device by an arrangement of lowpower radio devices may be reduced.

Interference from a first low power radio device in the arrangement maybe reduced by the first low power radio device: a) detecting thepolarization of an antenna of the further radio device and b)controlling the polarization of a transmitted radio signal in dependenceon the detected polarization. Interference from a second low power radiodevice in the arrangement may be reduced by the second low power radiodevice: a) receiving a radio signal and b) controlling the polarizationof a transmitted radio signal in dependence on the polarization of thereceived radio signal.

Advantageously, the controlling of the polarization of a transmittedradio signal by the first and second low power radio devices may lead tothe radio signals transmitted by the first and second low power radiodevices having substantially the same polarization, so the amplitude ofthe radio signals received at the second and first low power radiodevices is maximised.

According to a sixth aspect of the present invention, there is provideda chipset for use in a low power radio device having an antenna forreceiving radio signals comprising two non-parallel elements, thechipset comprising: means for receiving a first signal from a firstantenna element and for receiving a second signal from a second antennaelement; means for processing the received first and second signals todetermine the polarization of a radio signal incident upon the antenna;means for changing the effective polarization of the antenna to changethe polarization of low power radio signals transmitted by the antennain dependence on the polarization of the incident radio signal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference will nowbe made by way of example only to the accompanying drawings in which:

FIG. 1 illustrates a UWB device;

FIG. 2 illustrates a UWB radio system/arrangement comprising two UWBdevices, and a nearby cellular mobile terminal communicating with acellular base station; and

FIG. 3 illustrates a dual polarized wedge dipole suitable for use in aUWB device.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The Figures illustrate a low power radio device 10, operable in a firstradio system 100, comprising: a detector 12, 14 for detecting thepolarization of an antenna 221 of a further radio device 220, operatingin a further radio system 200, different to the first radio system 100;and a transmitter 12 for controlling the polarization of a transmittedradio signal 13 in dependence on the detected polarization.

FIG. 1 is a schematic illustration of a UWB device 10. The UWB device 10may be hand portable. The UWB device comprises a radio frequencytransceiver 12, a processor 14, a user input 16, a memory 18 and anoutput 20.

The transceiver 12 comprises a transmitter, a receiver and an antenna 17and is operable to transmit and receive UWB radio frequency signals. Theprocessor 14 is connected to receive an input from the transceiver 12and the user input 16 and to read from the memory 18, and to provide anoutput to the transceiver 12 and the output 20, and to write to thememory 18. The user input 16 may, for instance, comprise a keypad orother device for user input. The output is for conveying information toa user and may, for instance, comprise a display. The input 16 and theoutput 20 may be combined, for instance, in a touch sensitive displaydevice.

FIG. 2 illustrates a UWB radio arrangement/system 100 comprising a firstUWB device 10 in communication with a second UWB device 22. The secondUWB device 22 in this example takes the same form as the first UWBdevice 10 illustrated in FIG. 1. The antenna of the second UWB device 22has been denoted using the reference numeral 19 in FIG. 2 for clarity,but it may take the same form as the antenna 17 of the first UWB device10. FIG. 2 also illustrates a portion of a cellular radio system 200comprising a cellular base station 210 in communication with a cellularmobile terminal 220.

In FIG. 2, the complex vector h _(A) represents the antenna polarizationand directional gain properties of a given device A. The skilled readerwill be aware that h _(A) is a function of the three dimensionalincident or departure angles (ū_(R), ū_(T))(radial vectors) of the radiowaves that are transmitted or received by device A (i.e. h _(A) (ū_(R))and h _(A) (ū_(T))). H _(B,C) represents the radio wave propagationeffect of a signal B that is received by a device C and transmitted bydevice A. H _(B,C) is a dyadic tensor or matrix, which transforms atransmitted polarization vector to another vector representing the planewave electric field component that is received at the receiving antenna.

The first UWB device 10, in this example, is positioned close to thesecond UWB device 22 and also the cellular mobile terminal 220. Adistance of less than ten metres separates the first UWB device 10 andthe second UWB device 22, and the first UWB device 10 and the cellularmobile terminal 220. The cellular mobile terminal 220 is typicallypositioned within a distance of a few kilometres from the cellular basestation 210.

The cellular base station 210 communicates with the cellular mobileterminal 220 by transmitting a downlink signal 212. The downlink signal212 may be transmitted by the base station 210 in a number of differentdirections. The reference numeral 212 a denotes the portion of thetransmitted downlink signal 212 that travels from the base station 210to the mobile terminal 220.

The mobile terminal 220 communicates with the base station 210 bytransmitting an uplink signal 222. The uplink signal 222 transmitted bythe mobile station 220 may also be transmitted in a number of differentdirections. The reference numeral 222 a denotes the portion of thetransmitted uplink signal 222 that travels from the cellular mobileterminal 220 to the base station 210.

The first UWB device 10 may communicate with the second UWB device 22 bytransmitting a first UWB signal 13. The UWB signal 13 may be transmittedby the first UWB device 10 in a number of different directions. Thereference numeral 13 a denotes the portion of the first UWB signal 13that travels from the first UWB device 10 to the second UWB device 22.The second UWB device 22 may communicate with the first UWB device 10 bytransmitting a second UWB signal 15. Similarly, the reference numeral 15a denotes the portion of the second UWB signal 15 that travels from thesecond UWB device 22 to the first UWB device 10.

Each of the signals 13, 15, 212 and 222 comprise electromagnetic radiowaves having a particular polarization. The polarization of anelectromagnetic wave is determined by the change in the orientation ofits electric field vector over time.

An electromagnetic wave is said to be linearly polarized if thedirection of its electric field vector oscillates in a single plane. Anelectromagnetic wave is vertically polarized if it has a linearpolarization that is perpendicular to the Earth's surface. Anelectromagnetic wave is horizontally polarized if it has a linearpolarization that is parallel to the Earth's surface.

Where an antenna is linearly polarized, the polarization of atransmitted radio wave will be the same as the polarization of thetransmitting antenna. For example, if the transmitting antenna isvertically polarized, the transmitted radio wave will also be verticallypolarized.

Other types of polarization include circular polarization and ellipticalpolarization. If an electromagnetic wave is composed of two plane wavesof equal amplitude differing in phase by 90°, then the electromagneticwave is said to be circularly polarized. This is because thesuperposition of the two plane waves produces a resultantelectromagnetic wave with an electric field vector that traces out acircle over time.

If two plane electromagnetic waves of differing amplitude are related inphase by 90°, or if the relative phase is other than 90°, theelectromagnetic wave is said to be elliptically polarized. This isbecause the superposition of the two plane waves produces a resultantelectromagnetic wave with an electric field vector that traces out anellipse over time.

The transmitting antenna 211 at the base station 210 may, for instance,be a linearly polarized vertical antenna, or an antenna with apolarization of 45° to the vertical. Other polarizations are, however,possible. The base station 210 may also have a dual-polarized antennasetup, comprising two orthogonal antenna elements such as a verticalantenna element and a horizontal antenna element.

If there is a line of sight between the base station 210 and thecellular mobile terminal 220, the polarization of the downlink signalportion 212 a received at the mobile terminal 220 will be the same whenit is received at the mobile terminal 220 as the polarization of thedownlink signal 212 originally transmitted by the base station 210.

If the downlink signal portion 212 a has been reflected before itreaches the mobile terminal 220, the polarization of the downlink signal212 a when it is received by the mobile terminal 220 may be different tothe polarization of the downlink signal 212 originally transmitted bythe base station 210.

Reflection of a signal can also cause a signal to follow multipledifferent paths before it reaches a receiver. To enable the skilledreader to understand embodiments of the invention more easily, theanalysis below considers one signal component of the downlink signalportion 212 a, without considering multipath signals caused byreflection, for example. The narrow-band base station downlink signalportion 212 a received by the mobile terminal 220 in the one signal pathcase is given by:

V _(DL) = h _(MT) · H _(DL,MT) · h _(BS)  (1)

where the subscript DL represents the downlink signal portion 212 a thattravels from the base station 210 to the mobile terminal 220, thesubscript MT represents the mobile terminal 220 and the subscript BSrepresents the base station 210.

If we were to consider multipath propagation, the downlink signalportion 212 a would be given by:

V _(DL) =∫∫ h _(MT)(ū _(R))· H _(DL,MT)(ū _(T) , ū _(R))· h _(BS)(ū_(T))dū _(T) dū _(R)  (2)

where ū_(T) is the angle of transmission of the downlink signal portion212 a by the base station 210 and ū_(R) is the angle of reception of thedownlink signal portion 212 a by the mobile terminal 220.

The antenna 221 of the cellular mobile terminal 220 also has apolarization. The amplitude of the signal received by the mobileterminal 220 is maximised if the polarization of the antenna 221 of themobile terminal 220 matches that of the downlink signal portion 212 athat is incident upon it. The amplitude of the received signal dependsupon the orientation of the receiving antenna in comparison to theincident wave.

The first UWB device 10 may communicate with the second UWB device 22 bytransmitting a UWB signal 13. The portion of the signal 13 that travelsfrom the first UWB device 10 to the second UWB device 22 is denoted withthe reference numeral 13 a. If the receiver of the mobile terminal 220is operable to receive signals of the same frequency as the frequency ofthe UWB signal 13, when the UWB signal 13 is transmitted, a portion 13 bof the transmitted UWB signal 13 may inadvertently be received by themobile terminal 220. The UWB signal portion 13 b may therefore causeinterference at the mobile terminal 220 when it is receiving thedownlink signal portion 212 a from the base station 210.

The UWB signal portion 13 b transmitted by the first UWB device 10 andreceived at the mobile cellular terminal 220 is given by:

V _(UWB) ₁ _(,MT) = h _(MT) · H _(UMB) ₁ _(,MT) · h _(UMB) ₁   (3)

where the subscript UWB₁ denotes the first UWB device 10 or the UWBsignal portion 13 b transmitted by the first UWB device 10 and receivedat the mobile terminal 220.

While UWB signals are generally transmitted at a very low power so as tominimise any potential interference, a significant interference effectat the mobile terminal 220 can occur, particularly if: a) the downlinksignal portion 212 a has been reduced significantly in power when it isreceived at the cellular mobile terminal 220, for example because themobile terminal 220 is positioned a long distance from the base station210 or because reflection and refraction of the signal portion 212 aalong its path have reduced its power, and/or if: b) the first UWBdevice 10 is positioned very close to the mobile terminal 220 (i.e.within a distance of a few metres).

If the antenna properties and alignment of the mobile terminal 220(characterised by h _(MT)) and the change in polarization of the UWBsignal portion 13 b between the transmission of the signal 13 by thefirst UWB device 10 and the reception of the UWB signal portion 13 b bythe mobile terminal 220 (characterised by H _(UWB) ₁ _(,MT)) were knownby the first UWB device 10, it could transmit a radio signal with apolarization corresponding to:

h _(UMB) ₁ = H _(UMB) ₁ _(MT) ⁻¹·(ū _(R) × h _(MT))  (4)

In this case, the UWB signal portion 13 b is not received by thecellular terminal 220 because, from equation (3), it follows that:

V _(UWB) ₁ _(,MT) = h _(MT) · H _(UMB) ₁ _(,MT)·( H _(UMB) ₁ _(MT) ⁻¹·(ū_(R) × h _(MT)))= h _(MT)(ū _(R) × h _(MT))=0  (5)

h _(MT) and H _(UMB) ₁ _(,MT), however, are not generally known by theUWB device 10, so it cannot simply produce a radio signal according toequation (5).

The mobile station 220 also communicates with the base station 210 bytransmitting an uplink signal 222. The uplink signal 222 has the samepolarization as the transmitting antenna 221 of the mobile terminal 220.If the same antenna 221 is used for receiving signals as fortransmitting signals by the mobile terminal 220, the polarization of theuplink signal 222 is the same as the polarization of the antenna used toreceive signals by the mobile terminal 220.

A portion 222 b of the uplink signal 222 travels from the mobileterminal 220 to the first UWB device 10. As there is a line of sightbetween the first UWB device 10 and the mobile terminal 220, thepolarization of the uplink signal portion 222 b received at the firstUWB device 10 is then substantially the same as the originallytransmitted uplink signal 222. The polarization of the UWB signalportion 13 b received at the mobile terminal 220 also has thesubstantially the same polarization as the originally transmitted UWBsignal 13.

The electric field Ē_(UL,UWB) ₁ corresponding to the uplink signal 222 bthat is to be received by the antenna 17 of first UWB device 10 can berepresented in terms of the radio wave propagation effect H _(UL,UWB) ₁and the antenna vector h _(MT), as:

Ē _(UL,UWB) ₁ = H _(UL,UWB) ₁ · h _(MT)  (6)

If the electric field Ē_(UL,UWB) ₁ is detected by the first UWB device10, it can transmit a UWB radio signal 13 having a polarizationcorresponding to:

h _(UWB) ₁ =ū _(T) ×Ē _(UL,UWB) ₁ =ū _(T)×( H _(UL,UWB) ₁ · h_(MT))  (7)

A UWB signal 13 according to equation (7) has a polarization that isorthogonal to, or mismatched with, the polarization of the detecteduplink signal portion 222 b. From equation (3), it follows that the UWBsignal portion 13 b received by the mobile terminal 220 is:

V _(UWB) ₁ _(,MT) = h _(MT) · H _(UWB) ₁ _(,MT) [ū _(T)×( H _(UL,UWB) ₁· hMT)]  (8)

If we approximate the propagation medium to be isotropic, and there is aline of sight between the first UWB device 10 and the cellular mobileterminal 220:

H _(UL,UWB) ₁ = HUWB ₁ _(,MT {tilde over (=)}) I  (9)

where I is an identity matrix. It then follows that:

V_(UWB) ₁ _(,MT)=0  (10)

and hence the interference caused by the UWB signal portion 13 b at themobile terminal 220 is zero.

The interference at the mobile terminal 220 caused by the UWB signalportion 13 b can therefore be minimised if the polarization of thetransmitted UWB signal 13 is carefully controlled to be orthogonal tothe downlink signal portion 222 a that is received at the mobileterminal 220.

Where the mobile terminal 220 has a linearly polarized antenna and theUWB signal 13 is also linearly polarized, if the UWB signal portion 13 bhas a polarization at the antenna 221 of the mobile terminal 220 whichis orthogonal to the polarization of the antenna 221 of the mobileterminal 220, the UWB signal portion 13 b will not theoretically bereceived by the mobile terminal 220.

Where the mobile terminal 220 has a circularly polarized antenna and theUWB signal 13 is also circularly polarized, if the UWB signal portion 13b has a polarization at the antenna 221 of the mobile terminal 220 whichis maintained orthogonal to the polarization of the antenna 221 of themobile terminal 220, the UWB signal portion 13 b may not be detected bythe mobile terminal 220.

The closer the polarization of the UWB signal portion 13 b is to beingorthogonal to the receiving antenna of the mobile terminal 220 when itreaches the mobile terminal 220, the smaller the amplitude of thereceived UWB signal portion 13 b will be at the mobile terminal 220, andsmaller level of the interference caused by the UWB signal portion 13 bat the mobile terminal 220 will be.

The detection of the polarization of the antenna 221 of the mobileterminal 220 and the controlling of the effective polarization ofantenna 17 of the UWB device 10 may be initiated by a user. The user mayuse the user input 16 to request the detection of nearby radio devicesthat the UWB device 10 has the potential to interfere with. The user maythen instruct the device 10 to control its effective polarization tominimise interference. Alternatively, the UWB device 10 mayautomatically detect the polarization of the antenna 221 of the mobileterminal 220 and control the effective polarization of its antenna 17without user intervention.

The process of detecting the polarization of the antenna 221 of themobile terminal 220 and controlling the effective polarization of theantenna 17 of the UWB device 10 may occur before a UWB signal 13 istransmitted by the UWB device 10.

The UWB device 10 may attempt to detect signals from other radio devicesperiodically, to circumvent any possible interference problems at thoseradio devices. It may be the case that the mobile terminal 220 is not inthe vicinity of the UWB device 10 when the UWB device 10 beginstransmitting UWB signals, but is later brought close to the UWB device10. In this situation, the UWB device 10 detects the polarization of theantenna 221 of the mobile terminal 220 and adapts the effectivepolarization of its antenna 17 to minimise or reduce interference withthe mobile terminal 220.

While in practice it may be difficult to ensure that the UWB signal 13has a polarization that is precisely orthogonal to the polarization ofthe antenna 221 of the mobile terminal 220, in reality a 10 to 15 dBinterference reduction can be achieved.

A portion 13 a of the first UWB signal 13 is received by the second UWBdevice 22. In order to maximise the amplitude of the signal portion 13 athat is received at the second UWB device 22, the second UWB device 22matches the effective polarization of its antenna 19 to the effectivepolarization of the antenna 17 of first UWB device 10 and thepolarization of the first UWB signal 13.

The second UWB device 22 transmits a second UWB signal 15. A portion of15 a of the second UWB signal 15 is received by the first UWB device 10.The matching of the effective polarization of the antenna of the secondUWB device 22 has the effect of reducing the interference caused at themobile terminal 220 by a portion 15 b of the second UWB signal 15 thatmay be received at the mobile terminal 220 as the effective polarizationof the antenna 19 of the second UWB device 22, when matched with theeffective polarization of the antenna 17 of the first UWB device 10, isorthogonal to the polarization of the antenna 221 of the mobile terminal220.

In the case where the each UWB device 10, 22 has two or more separateantennas for transmitting and receiving, the effective polarization ofthe transmitting and receiving antennas of both of the UWB devices 10,22 are matched, so that the effective polarization of all of theantennas are the same.

The second UWB device 10 may achieve the polarization match in a numberof ways. The second UWB device 22 may go through the same process ofdetecting the mobile terminal 220 through a portion of the uplink signal222 and mismatching the effective polarization of its antenna 19 withthe detected uplink signal portion as the first UWB device 10. In thiscase, if there is a line of sight between the first UWB device 10 andmobile terminal 210 and the second UWB device 22 and mobile terminal220, the effective polarization of the antennas 17, 19 of the first andsecond UWB devices 10, 22 are the same.

Alternatively, the second UWB device 22 may detect the polarization ofthe portion 13 a of the UWB signal 13 and match the effectivepolarization of its antenna 19 with that of the UWB signal portion 13 a.In this case, the effective polarization of the antenna 19 of the secondUWB device 22 will be the same as that of the antenna 17 of the firstUWB device 10, provided that there is a line of sight between the firstand second UWB devices 10, 22. Furthermore, provided that a line ofsight also exists between the second UWB device 22 and the mobileterminal 220, the effective polarization of the antenna 19 of the UWBdevice 22 and therefore the polarization of the second transmitted UWBsignal 22 will be orthogonal to, or mismatched with, the antenna 221 ofthe mobile cellular terminal 220.

A line of sight between the first UWB device 10 and the second UWBdevice 22 can be assumed in most cases, because the power of thetransmitted UWB signals 13, 15, is so low. If there is no line of sightbetween the UWB devices 10, 22 no signal will be received by thereceiving device, in most instances, or the signal will be received onlyat a very low level.

Alternatively, the first UWB device 10 can communicate the effectivepolarization of its antenna to the second UWB device 22 in the first UWBsignal 13. In order to communicate its effective polarization, the firstUWB device 10 may need to know its orientation. This could be achievedby using gravity and/or acceleration sensors to find out the orientationof the UWB device 10 with respect to the gravity. If the second UWBdevice 22 also has gravity or acceleration sensors to find itsorientation, it can align the effective polarization of its antenna 19with that of the first UWB device 10.

In a situation where there is more than one device at which thetransmission of UWB signals 13, 15 could cause interference (i.e. thereis more than one device in the vicinity of the UWB devices 10, 22), theUWB devices 10, 22 may communicate with each other to determine which ofthe other devices is most relevant when considering how the polarizationof transmitted UWB signals 13, 15 should be orientated. The decision asto how the polarization should be orientated may be based upon theamplitude of the signals made by the other devices at the UWB devices10,22.

For instance, if there are two mobile terminals in the vicinity of theUWB devices 10, 22, but the detected uplink signal portion 222 b, 222 cat the UWB devices 10, 22 is higher for a first one of the mobileterminals than for a second, the UWB devices may choose to mismatch thepolarization of the UWB signals 13, 15 they transmit with the antenna ofthe first mobile terminal, and not the second.

FIG. 3 illustrates a dual-polarized wedge dipole antenna 17/19 for usein the UWB devices 10, 22. The dual-polarized wedge dipole antenna 17/19comprises four wedge-shaped portions, 51, 52, 53 and 54, and is part ofthe transceiver 12. The portions 51 to 54 take the form of isoscelestriangles.

Wedge portions 51 and 53 form a first antenna element 55. Wedge portions52 and 54 form a second antenna element 56, which has a polarizationthat is orthogonal to that of the first antenna element 55. Thepolarization of an electromagnetic wave incident upon the wedge dipoleantenna 17/19 may be found by measuring how the amplitude and phase ofthe signals received on each antenna element 55, 56 relate to eachother.

Computer program instructions for controlling the effective polarizationof the wedge dipole antenna 17/19 are stored in the memory 18. When thecomputer program instructions are loaded into the processor 14, the UWBdevice 10, 22 changes the effective polarization of the wedge dipoleantenna 17/19 when transmitting signals by applying a different level ofgain and/or by applying a different delay to the signal applied to eachdifferent antenna element 55, 56. If the UWB device 10, 22 is configuredto transmit a linearly polarized wave, solely changing the gain willcause the antenna 17/19 to transmit a linearly polarised wave with adifferent polarization angle. Changing the delay will result in a phaseshift between the signal components applied to each different wedge 51to 54, and the transmitted wave will be circularly or ellipticallypolarized. The UWB device 10, 22 changes the effective polarization ofthe wedge dipole antenna 17/19 when receiving signals by applying adifferent level of gain and/or by applying a delay to the signalreceived from each different wedge 51 to 54.

The computer program instructions may arrive at the UWB devices 10, 22via an electromagnetic carrier signal or be copied from a physicalentity such as a computer program product, a memory device or a recordmedium such as a CD-ROM or DVD.

Although embodiments of the present invention have been described in thepreceding paragraphs with reference to various examples, it should beappreciated that modifications to the examples given can be made withoutdeparting from the scope of the invention as claimed. For example,embodiments of the invention have been described above in relation toUWB devices, but could be applied to any other type of low power radiodevice that is capable of causing interference. The device that maypotentially suffer from interference in the above description was acellular mobile terminal 220, which was part of a cellular system 200.The skilled person will appreciate that embodiments of the inventioncould be used to alleviate potential interference problems at othertypes of radio device operating in other radio systems, such as thoseoperating in an 802.11 WLAN network, or a Bluetooth system.

Furthermore, the UWB devices 10,22 described in the description comprisea processor 14. As an alternative to the processor 14, or in addition tothe processor 14, the UWB devices 10,22 may comprise a chipset. Thechipset may comprise one or more integrated circuits.

While the above description describes a preferred implementation, itshould be appreciated that benefits of the invention may be obtained byvarying the described implementation. Although in the preceding example,a linear polarization for a signal 13 produced by the first UWB device10 is controlled to be orthogonal to the polarization of the antenna ofthe cellular mobile terminal 220, it should be appreciated that this isan optimal solution. Benefits may be obtained by controlling thepolarization of the signal 13 so that it has a reduced componentparallel to the polarization of the antenna 221, but is not necessarilyorthogonal to it.

Whilst endeavouring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon.

1. A radio device, configured to operate in a first radio system,comprising: a detector configured to detect the polarization of anantenna of a further radio device operating in a further radio systemdifferent from the first radio system; and a transmitter configured tocontrol the polarization of a transmitted radio signal in dependence onthe detected polarization.
 2. A radio device as claimed in claim 1,wherein the polarization of the transmitted signal is controlled to besubstantially orthogonal to the polarization of the antenna of thefurther radio device.
 3. A radio device as claimed in claim 1, whereinthe transmitter has a first effective polarization for transmitting afirst radio signal having a first polarization, and is configured tochange its effective polarization in dependence on the detectedpolarization, from the first effective polarization to a secondeffective polarization for transmitting a second radio signal having asecond polarization, wherein the second polarization is different fromthe first polarization.
 4. A radio device as claimed in claim 3, whereinthe second polarization is substantially orthogonal to the polarizationof the detected polarization.
 5. A radio device as claimed in claim 1,wherein the detector is configured to detect the polarization of theantenna of the further radio device by detecting the polarization of aradio signal transmitted by the further radio device.
 6. A radio deviceas claimed in claim 5, wherein the radio signal transmitted by thefurther radio device has a substantially linear polarization.
 7. A radiodevice as claimed in claim 5, wherein the radio signal transmitted bythe further radio device has a circular polarization.
 8. A radio deviceas claimed in claim 5, wherein the radio signal transmitted by thefurther radio device has an elliptical polarization.
 9. A radio deviceas claimed in claim 5, further comprising an antenna configured toreceive the radio signal transmitted by the further radio device usingtwo non-parallel antenna elements, wherein the radio signal received byeach antenna element has an amplitude and a phase, and wherein the radiodevice is configured to determine the polarization of the received radiosignal based on the values of the amplitude and phase of the radiosignals received at the respective antenna elements.
 10. A radio deviceas claimed in claim 5, wherein the detector is configured to detect aradio signal transmitted by the further radio device having a frequencysituated within a frequency range that the radio device is configured totransmit in.
 11. A radio device as claimed in claim 1, wherein the radiosignal transmitted by the radio device is for a first radio system andfor reception by a second radio device operating in the first radiosystem.
 12. A radio device as claimed in claim 1, wherein the firstradio system operates using Ultra Wide Bandwidth (UWB) signals.
 13. Aradio device as claimed in claim 1, wherein the further radio system hasdifferent operating protocols from the first radio system.
 14. A radiodevice as claimed in claim 1, wherein the further radio system is aradio telephone system.
 15. A radio device as claimed in claim 5,wherein the further radio system is a cellular telephone system and theradio signal transmitted by the further radio device is for reception bya cellular base station.
 16. A method comprising: detecting thepolarization of an antenna of a radio device operating in a furtherradio system different from a first radio system; and controlling thepolarization of a transmitted radio signal for the first radio system independence on the detected polarization.
 17. An article of manufacture,comprising: a computer-readable medium containing computer-readablecode, which when executed by a computer causes the computer to, receivea first signal from a first antenna element and a second signal from asecond antenna element; process the received first and second signals todetermine the polarization of a radio signal incident upon the antenna;and change the effective polarization of the antenna to change thepolarization of radio signals transmitted by the antenna in dependenceon the polarization of the incident radio signal.
 18. A systemcomprising: a first radio device and a second radio device, configuredto operate in a first radio system, wherein, the first radio devicecomprises, a detector configured to detect the polarization of anantenna of a further radio device operating in a further radio systemdifferent from the first radio system; and a transmitter configured tocontrol the polarization of a transmitted radio signal in dependence onthe detected polarization; and wherein, the second radio devicecomprises, a receiver configured to receive a radio signal; and atransmitter configured to control the polarization of a transmittedradio signal in dependence on the polarization of the received radiosignal.
 19. A system as claimed in claim 18, wherein a radio signalreceived by the receiver of the second radio device is a radio signaltransmitted by the first radio device.
 20. A system as claimed in claim19, wherein the polarization of a radio signal transmitted by the secondradio device is controlled by the transmitter of the second radio deviceto substantially match the polarization of a radio signal received bythe second radio device.
 21. A system as claimed in claim 19, whereinthe receiver of the second radio device comprises a detector fordetecting the polarization of the received signal.
 22. A system asclaimed in claim 19, wherein a radio signal transmitted by the firstradio device and received by the second radio device containsinformation regarding its polarization.
 23. A system as claimed in claim18, wherein a radio signal received by the receiver of the second radiodevice is a radio signal transmitted by the further radio device.
 24. Asystem as claimed in claim 23, wherein the polarization of a radiosignal transmitted by the second radio device is controlled by thetransmitter of the second radio device to be substantially orthogonal tothe polarization of the radio signal received by the second radiodevice.
 25. A method, comprising the steps of: detecting, at a firstradio device of a first radio system, a polarization of an antenna of afurther radio device operating in a further radio system different fromthe first radio system; controlling, at the first radio device, apolarization of a transmitted radio signal in dependence on the detectedpolarization; receiving a radio signal at a second radio device of thefirst radio system; and controlling, at the second radio device, apolarization of a transmitted radio signal in dependence on thepolarization of the received radio signal.
 26. A chipset, comprising:means for receiving a first signal from a first antenna element and asecond signal from a second antenna element; means for processing thereceived first and second signals to determine the polarization of aradio signal incident upon an antenna; and means for changing theeffective polarization of the antenna to change the polarization ofradio signals transmitted by the antenna in dependence on thepolarization of the incident radio signal.
 27. A method as claimed inclaim 16, wherein the polarization of the transmitted signal iscontrolled to be substantially orthogonal to the polarization of theantenna of the radio device operating in the further radio system.
 28. Amethod as claimed in claim 16, wherein detecting the polarization of theantenna of the radio device operating in the further radio systemincludes detecting the polarization of a radio signal transmitted by theradio device.
 29. A method as claimed in claim 28, wherein the radiosignal transmitted by the radio device has a substantially linearpolarization.
 30. A method as claimed in claim 28, wherein the radiosignal transmitted by the radio device has a circular polarization. 31.A method as claimed in claim 28, wherein the radio signal transmitted bythe radio device has an elliptical polarization.
 32. A method as claimedin claim 28, further comprising: receiving the radio signal transmittedby the radio device, via an antenna with two non-parallel antennaelements, wherein the radio signal received by each antenna element hasan amplitude and a phase; and determining the polarization of thereceived radio signal based on the amplitude and the phase of the radiosignals received at the respective antenna elements.
 33. A method asclaimed in claim 16, further comprising: detecting a radio signaltransmitted by the further radio device having a frequency situatedwithin a frequency range that the first radio system is configured totransmit in.
 34. A method as claimed in claim 16, wherein the firstradio system is a short-range wireless communication network and thefurther radio system is a cellular communication network.
 35. A radiodevice as claimed in claim 1, wherein the first radio system is ashort-range wireless communication network and the further radio systemis a cellular communication network.